In practically all existing types of single-shaft hinges, a resin or metal cam and a coil spring or plate spring are assembled as a single set and rotary frictional torque is generated in a condition with two cam sets in pressure contact (for example Japanese Patent Application Publication No. 10-311327 and Japanese Patent Application Publication No. 2000-22790).
In recent years, as increasing importance has been attached to ease of operation and feeling during rotation, there has been a strong demand for hinge components with highly precise torque value control, durability capable of withstanding some hundreds of thousands of operations, smaller size and lighter weight and reduced cost.
In conventional products, rotary frictional torque is generated solely by pressure contact of a pair of a fixed cam and rotary cam, so, typically the restoring force of the spring would be increased in order to satisfy demands for smaller size and lighter weight and to generate larger rotary torque than conventionally.
However, in cam portions that have been made of very small size to meet such demands for size reduction, a higher surface pressure than conventionally must be borne in this very small area, so inevitably a material of excellent wear resistance and components of high dimensional precision become necessary.
Consequently, conventional hinge components had the drawback that when there were variation in the wear resistance or dimensions, this resulted in severe variability of the torque value or aging deterioration (frictional wear) of the cam section, causing a lowered torque value or failure.